I had one server that was in production suddenly become no longer responsive w.r.t network. No settings have been changed in a while, so I don't really understand why it would go wrong. It looks like a routing issue, but don't know how to progress from here.

I tried loading rescue cd and seeing if there's any hardware issue, but temporary OS had no issue connecting via network.

Here are some info: (to note, eth0 is what I use for lan, eth1 is what I use for internet)

Can you post your /etc/sysconfig/network and a traceroute/tracepath to some external IP (like google's DNS)? Do you define your default gateway in an interface instead of /etc/sysconfig/network? Can you ping your default gateway?
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dawudMay 13 '13 at 6:33

@dawud, I've edited my original post to include more information.
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GrumpyMay 13 '13 at 6:45

Can you ping any other IP's in the subnet? i.e. 149.255.34.170, 149.255.34.171, 149.255.34.172, 149.255.34.174?
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Jaz005May 13 '13 at 7:04

@Jaz005, any address that's not 192.* or localhost will result in Destination Host Unreachable.
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GrumpyMay 13 '13 at 7:11

1

If you still can't ping your gateway on the same network, this is probably a layer 2 issue. Is this a physical or virtual host? if the former, contact the people administering the network to check if your MAC appears in the switch port is should; if the latter, the same applies, and also check if the udev rules are OK
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dawudMay 13 '13 at 8:26

Though other sys admins have looked at the server, no one was able to find any software related issue. I suspect it was an ethernet adapter failure and so does the host. A brand new server replaced it to come to a solution.